Recombinant therapeutic proteins are produced by many different methods. One preferred method is production of recombinant proteins from mammalian host cell lines. Cell lines, such as Chinese Hamster Ovary (CHO) cells, are engineered to express the therapeutic protein of interest. Different cell lines have advantages and disadvantages for recombinant protein production, including protein characteristics and productivity. Selection of a cell line for commercial production often balances the need for high productivity with the ability to deliver consistent product quality with the attributes required of a given product. One important class of therapeutic recombinant proteins that require consistent, high quality characteristics and high titer processes are monoclonal antibodies.
Monoclonal antibodies produced in mammalian host cells can have a variety of post-translational modifications, including glycosylation. Monoclonal antibodies, such as IgG1s, have an N-linked glycosylation site at asparagine 297 (Asn297) of each heavy chain (two per intact antibody). The glycans attached to Asn297 on antibodies are typically complex biantennary structures with very low or no bisecting N-acetylglucosamine (bisecting GIcNAc) with low amounts of terminal sialic acid and variable amounts of galactose. The glycans also usually have high levels of core fucosylation. Reduction of core fucosylation in antibodies has been shown to alter Fc effector functions, in particular Fcgamma receptor binding and ADCC activity. This observation has lead to interest in the engineering cell lines so they produce antibodies with reduced core fucosylation.
Methods for engineering cell lines to reduce core fucosylation included gene knock-outs, gene knock-ins and RNA interference (RNAi). In gene knock-outs, the gene encoding FUT8 (alpha 1,6-fucosyltransferase enzyme) is inactivated. FUT8 catalyzes the transfer of a fucosyl residue from GDP-fucose to position 6 of Asn-linked (N-linked) GlcNac of an N-glycan. FUT8 is reported to be the only enzyme responsible for adding fucose to the N-linked biantennary carbohydrate at Asn297. Gene knock-ins add genes encoding enzymes such as GNTIII or a golgi alpha mannosidase II. An increase in the levels of such enzymes in cells diverts monoclonal antibodies from the fucosylation pathway (leading to decreased core fucosylation), and having increased amount of bisecting N-acetylglucosamines. RNAi typically also targets FUT8 gene expression, leading to decreased mRNA transcript levels or knock out gene expression entirely.
Alternatives to engineering cell lines include the use of small molecule inhibitors that act on enzymes in the glycosylation pathway. Inhibitors such as catanospermine act early in the glycosylation pathway, producing antibodies with immature glycans (e.g., high levels of mannose) and low fucosylation levels. Antibodies produced by such methods generally lack the complex N-linked glycan structure associated with mature antibodies.
In contrast, the present invention provides small molecule fucose analogs for use in producing recombinant antibodies that have complex N-linked glycans, but have reduced core fucosylation.